Kyra Sedgwick by Karen Neal/TNT; Mary-Louise Parker by Sonja Flemming/Showtime
Feel that change of seasons? Hard not to notice on this Monday night, as two of cable's best summer series- TNT's popular signature drama The Closer and Showtime's quirky classic Weeds- sign off with life-or-death cliffhangers, a week before the official network season gets underway. ( The Closer's story will pick up again in the new year, with five episodes remaining in this split season.)

You really can't do better tonight than the shattering Closer finale, which pulls off an uncanny shift in tone from early scenes of gallows humor to a building sense of unease and desperation, culminating in a breathlessly harrowing climactic event involving all of the major players in the newly named Major Crimes Division. (Last week, Deputy Chief Brenda Leigh Johnson's Priority Homicide unit was shut down after a public-relations scandal, though the team itself was kept intact thanks to some fancy footwork on Brenda's part. Like you thought they'd dissolve this group.)

Emmy nominee Kyra Sedgwick keeps the tone light in the opening scenes when a grisly crime scene suddenly becomes a potential bomb site, and her stubbornness about leaving the scene turns into a bit of slapstick theater, as she's hauled out "like a sack of potatoes" (she gripes) while a slow-moving robotized UGV (unmanned ground vehicle, according to a fetishistic Tao) named "Babs" takes over. Brenda Leigh is not amused at being upstaged, but her colleagues are and so will you be.

The laughs don't last long, as the trail leads to a pack of chillingly insolent teens, reminiscent of the disaffected Columbine shooters, who have much more than petty mischief in mind. As one boasts, "My parents aren't smart enough to understand what I'm doing." As the reality of the situation dawns on Brenda and her team, racing the clock to figure out where the next calamity might strike, the stage is set for a suspenseful and explosive showdown. How it ends will likely leave you gasping and desperate for the next batch of episodes.

The Closer has enjoyed one of its better seasons this summer, with strong episodes for many of the supporting players- especially G.W. Bailey's gravelly Provenza and Anthony Denison as his wry sidekick Flynn, and in one of the more wrenching subplots, Raymond Cruz's Sanchez. Sedgwick is always a delight, closing her cases each week, sometimes by taking extreme measures (including last week's shocker), while muddling through her relationship with FBI guy Fritz (Jon Tenney). It will be a nice treat not to have to wait until next summer to see more of them all, quite possibly the best current ensemble in the cluttered world of the TV crime drama.

Meanwhile, over on Weeds, Nancy (Mary-Louise Parker) just continues to fall deeper into the abyss, more conflicted than ever over her passionate relationship with the deadly but amorous Tijuana mayor who now apparently has her life in his hands. (Last week's cliffhanger showed him supervising the grisly torture/demise of DEA Agent Till's partner- in several respects- Agent Schlatter, who before he died pointed the finger at Nancy.) It's a very eventful half-hour, full of mordant twists that are almost too appalling to qualify as comedy. And yet the darkest of humors has always informed nearly everything that happens on Weeds, which successfully reinvented itself this season as it put suburban satire behind it (with the torching of Agrestic) to focus on life on the border. The California-Mexico border, to be sure, but also the borderlands of morality and responsibility, of love and duty, of adolescence and sexuality, of fractured family, and as always of right and wrong, a line that has become so blurry on this show as to require corrective lenses.

Parker continues to amaze as she conveys Nancy's vulnerability and recklessness, her shame over where she's led her family and her tremulous fear over where her actions will take her next. The season's final moment delivers a bombshell that promises to make next season even more unpredictable. Weeds these days is as troubling as it is entertaining, and that's probably as it ought to be.